Hi Marina. What model did you buy? There isn’t really much to do in terms of maintenance. Keep it in its case to stop it getting dusty, and shake out the spit after you’ve played it. There’s a button to press somewhere at the end which lets it out. Good luck!
To add to Mikey’s post, re maintenance, don’t play immediately after eating, as little food particles can cause problems with the reeds inside. And also avoid sugary drinks while playing.
A case isn’t that important – I leave my melodicas out of their cases all the time with no problem. Could be handy for travelling though…
The Hohner piano 27s are very nice looking instruments – I have one, with its case. To be honest I don’t think you’re going to find a case on its own, might have to make one after all. Post a photo if you do!
If the melodica gets very dirty, you can remove the case to clean it separately. (Follow the instructions on “How to tune a melodica”). Don’t clean the reed plates – you can instead gently ‘ping’ (flick) each reed tongue a couple of times to remove any encrustations of saliva. Do this also if you have a note which isn’t sounding.